1. Field of the Invention
This invention relates to an electroacoustic transducer and more particularly to an electroacoustic transducer that has multisided flux plates used in connection with a differently shaped permanent magnet.
2. Description of the Prior Art
Ceramic or ferrite electroacoustic transducers, commonly known as loud speakers, have front and back flux plates, an annular magnet, a pole piece and a voice coil operatively connected to a diaphragm.
Conventionally, the front and back flux plates of an electroacoustic transducer are slightly smaller in contour shape and area than the magnet placed in between the two flux plates, and have the same contour shape as the magnet with the edges of the flux plates placed parallel to the edges of the magnet. The magnet and the flux plates have most commonly been circular in shape due to a high magnetic efficiency of the circular contour in maintaining a magnetic circuit.
An example of an electroacoustic transducer is disclosed in French patent to Audax, Brevet d'Invention No. 1,468,916 issued Jan. 2, 1967. In the Audax patent, a round front flux plate has a plurality of notches which correspond to projections in a collar in the rear face of the basket. The notches are placed in the front flux plate for attaching the yoke to the basket. The front flux plate is inserted through the collar and the yoke is twisted, locking the yoke into the collar. Another embodiment of the Audax reference discloses a tapered neck around the circular front pole piece with broad flattened notches formed on the neck. The pole piece then fits through a corresponding shaped collar in a basket and, when twisted, is locked to the collar. In the Audax reference, even though the flux plate has notches, the notches are placed away from the permanent magnet. Consequently, the surface of the flux plate which abuts the permanent magnet has the same contour shape as the permanent magnet.
In the loud speaker art, square flux plates with square magnets that have radial corners are also known. Except for the radial corner, the contour of the square flux plate is parallel to the edges of the square magnet. For all other shapes, the edges of the flux plate have always been placed parallel to the edges of the permanent magnet.